add support for LALR(1)

README.md

@@ -44,10 +44,10 @@ build = "build.rs" # LALRPOP preprocessing
 
 # Add a dependency on the LALRPOP runtime library:
 [dependencies.lalrpop-util]
-version = "0.1"
+version = "0.2.0"
 
 [build-dependencies.lalrpop]
-version = "0.1"
+version = "0.2.0"
 ```
 
 And create a `build.rs` file that looks like:

lalrpop-intern/Cargo.toml

@@ -1,4 +1,7 @@
 [package]
 name = "lalrpop-intern"
 version = "0.2.0" # LALRPOP
+description = "Simple string interner used by LALRPOP"
+repository = "https://github.com/nikomatsakis/lalrpop"
+license = "Unlicense"
 authors = ["Niko Matsakis <niko@alum.mit.edu>"]

lalrpop-test/src/expr_lalr.lalrpop

@@ -0,0 +1,32 @@
+grammar(scale: i32)["LALR(1)"];
+
+use util::tok::Tok;
+
+extern token {
+    enum Tok {
+        "(" => Tok::LParen(..),
+        ")" => Tok::RParen(..),
+        "-" => Tok::Minus(..),
+        "+" => Tok::Plus(..),
+        "*" => Tok::Times(..),
+        "/" => Tok::Div(..),
+        "Num" => Tok::Num(<i32>)
+    }
+}
+
+pub Expr = {
+    <l:Expr> "-" <r:Factor> => l - r;
+    <l:Expr> "+" <r:Factor> => l + r;
+    Factor;
+};
+
+Factor = {
+    <l:Factor> "*" <r:Term> => l * r;
+    <l:Factor> "/" <r:Term> => l / r;
+    Term;
+};
+
+Term: i32 = {
+    <n:"Num"> => n * scale;
+    "(" <Expr> ")";
+};

lalrpop-test/src/expr_lalr.rs

@@ -0,0 +1,5 @@
+#![allow(unused_imports)]
+#![allow(unused_variables)]
+use util::tok::Tok;
+extern crate lalrpop_util as __lalrpop_util;
+use self::__lalrpop_util::ParseError as __ParseError;

lalrpop-test/src/main.rs

@@ -7,6 +7,9 @@ mod sub;
 /// more interesting demonstration of parsing full expressions
 mod expr;
 
+/// more interesting demonstration of parsing full expressions
+mod expr_lalr;
+
 /// test that passes in lifetime/type/formal parameters and threads
 /// them through, building an AST from the result
 mod expr_arena;
@@ -54,6 +57,31 @@ fn expr_test5() {
     util::test(|v| expr::parse_Expr(11, v), "22 * 3 - 6", 22*11 * 3*11 - 6*11);
 }
 
+#[test]
+fn expr_lalr_test1() {
+    util::test(|v| expr::parse_Expr(1, v), "22 - 3", 22 - 3);
+}
+
+#[test]
+fn expr_lalr_test2() {
+    util::test(|v| expr::parse_Expr(1, v), "22 - (3 + 5)", 22 - (3 + 5));
+}
+
+#[test]
+fn expr_lalr_test3() {
+    util::test(|v| expr::parse_Expr(1, v), "22 - (3 - 5) - 13", 22 - (3 - 5) - 13);
+}
+
+#[test]
+fn expr_lalr_test4() {
+    util::test(|v| expr::parse_Expr(1, v), "22 * 3 - 6", 22 * 3 - 6);
+}
+
+#[test]
+fn expr_lalr_test5() {
+    util::test(|v| expr::parse_Expr(11, v), "22 * 3 - 6", 22*11 * 3*11 - 6*11);
+}
+
 #[test]
 fn sub_test1() {
     util::test(sub::parse_S, "22 - 3", 22 - 3);

lalrpop/src/build/mod.rs

@@ -25,12 +25,57 @@ fn process_dir<P:AsRef<Path>>(root_dir: P) -> io::Result<()> {
     let lalrpop_files = try!(lalrpop_files(root_dir));
     for lalrpop_file in lalrpop_files {
         let rs_file = lalrpop_file.with_extension("rs");
+        if try!(needs_rebuild(&lalrpop_file, &rs_file)) {
             let grammar = try!(parse_and_normalize_grammar(lalrpop_file));
             try!(emit_recursive_ascent(&rs_file, &grammar));
+            try!(make_read_only(&rs_file));
+        }
     }
     Ok(())
 }
 
+fn needs_rebuild(lalrpop_file: &Path,
+                 rs_file: &Path)
+                 -> io::Result<bool>
+{
+    return match fs::metadata(&rs_file) {
+        Ok(rs_metadata) => {
+            let lalrpop_metadata = try!(fs::metadata(&lalrpop_file));
+            Ok(compare_modification_times(&lalrpop_metadata, &rs_metadata))
+        }
+        Err(e) => {
+            match e.kind() {
+                io::ErrorKind::NotFound => Ok(true),
+                _ => Err(e),
+            }
+        }
+    };
+
+    #[cfg(unix)]
+    fn compare_modification_times(lalrpop_metadata: &fs::Metadata,
+                                  rs_metadata: &fs::Metadata)
+                                  -> bool
+    {
+        use std::os::unix::fs::MetadataExt;
+        lalrpop_metadata.mtime() >= rs_metadata.mtime()
+    }
+
+    #[cfg(not(unix))]
+    fn compare_modification_times(lalrpop_metadata: &fs::Metadata,
+                                  rs_metadata: &fs::Metadata)
+                                  -> bool
+    {
+        true
+    }
+}
+
+fn make_read_only(rs_file: &Path) -> io::Result<()> {
+    let rs_metadata = try!(fs::metadata(&rs_file));
+    let mut rs_permissions = rs_metadata.permissions();
+    rs_permissions.set_readonly(true);
+    fs::set_permissions(&rs_file, rs_permissions)
+}
+
 fn lalrpop_files<P:AsRef<Path>>(root_dir: P) -> io::Result<Vec<PathBuf>> {
     let mut result = vec![];
     for entry in try!(fs::read_dir(root_dir)) {

lalrpop/src/grammar/parse_tree.rs

@@ -18,6 +18,13 @@ pub struct Grammar {
     pub parameters: Vec<Parameter>,
     pub where_clauses: Vec<String>,
     pub items: Vec<GrammarItem>,
+    pub algorithm: Option<Algorithm>,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Algorithm {
+    pub span: Span,
+    pub text: InternedString,
 }
 
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]

lalrpop/src/grammar/repr.rs

@@ -4,7 +4,7 @@
  * representation incrementally.
  */
 
-use intern::{InternedString};
+use intern::{self, InternedString};
 use grammar::pattern::{Pattern};
 use std::fmt::{Debug, Display, Formatter, Error};
 use util::{map, Map, Sep};
@@ -21,6 +21,9 @@ pub struct Grammar {
     // that they do not conflict with any action strings
     pub prefix: String,
 
+    // algorithm user requested for this parser
+    pub algorithm: Algorithm,
+
     // these are the nonterminals that were declared to be public; the
     // key is the user's name for the symbol, the value is the
     // artificial symbol we introduce, which will always have a single
@@ -48,6 +51,12 @@ pub struct Grammar {
     pub types: Types,
 }
 
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum Algorithm {
+    LR1,
+    LALR1,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Parameter {
     pub name: InternedString,
@@ -323,3 +332,12 @@ impl Grammar {
     }
 }
 
+impl Algorithm {
+    pub fn from_str(s: InternedString) -> Option<Algorithm> {
+        intern::read(|r| match r.data(s) {
+            "LR" | "LR(1)" => Some(Algorithm::LR1),
+            "LALR" | "LALR(1)" => Some(Algorithm::LALR1),
+            _ => None,
+        })
+    }
+}

lalrpop/src/lr1/core/mod.rs

@@ -0,0 +1,156 @@
+//! Core LR(1) state construction algorithm.
+
+use kernel_set;
+use grammar::repr::*;
+use lr1::first;
+use lr1::{Action, Lookahead, Item, Items, State, StateIndex, TableConstructionError};
+use std::rc::Rc;
+use util::{map, Multimap, Set};
+
+#[cfg(test)] mod test;
+
+pub fn build_lr1_states<'grammar>(grammar: &'grammar Grammar,
+                                  start: NonterminalString)
+                                  -> Result<Vec<State<'grammar>>,
+                                            TableConstructionError<'grammar>>
+{
+    let lr1 = LR1::new(grammar);
+    lr1.build_states(start)
+}
+
+struct LR1<'grammar> {
+    grammar: &'grammar Grammar,
+    first_sets: first::FirstSets,
+}
+
+impl<'grammar> LR1<'grammar> {
+    fn new(grammar: &'grammar Grammar) -> LR1 {
+        LR1 {
+            grammar: grammar,
+            first_sets: first::FirstSets::new(grammar),
+        }
+    }
+
+    fn build_states(&self, start_nt: NonterminalString)
+                    -> Result<Vec<State<'grammar>>, TableConstructionError<'grammar>>
+    {
+        let mut kernel_set = kernel_set::KernelSet::new();
+        let mut states = vec![];
+
+        // create the starting state
+        kernel_set.add_state(
+            self.transitive_closure(
+                self.items(start_nt, 0, Lookahead::EOF)));
+
+        while let Some(items) = kernel_set.next() {
+            let index = StateIndex(states.len());
+            let mut this_state = State { index: index, items: items.clone(),
+                                         tokens: map(), gotos: map() };
+
+            // group the items that we can transition into by shifting
+            // over a term or nonterm
+            let transitions: Multimap<Symbol, Item<'grammar>> =
+                items.vec
+                     .iter()
+                     .filter_map(|item| item.shifted_item())
+                     .collect();
+
+            for (symbol, items) in transitions.into_iter() {
+                let items = self.transitive_closure(items);
+                let next_state = kernel_set.add_state(items);
+
+                match symbol {
+                    Symbol::Terminal(s) => {
+                        let action = Action::Shift(next_state);
+                        let prev = this_state.tokens.insert(Lookahead::Terminal(s), action);
+                        assert!(prev.is_none()); // cannot have a shift/shift conflict
+                    }
+
+                    Symbol::Nonterminal(s) => {
+                        let prev = this_state.gotos.insert(s, next_state);
+                        assert!(prev.is_none());
+                    }
+                }
+            }
+
+            // finally, consider the reductions
+            for item in items.vec.iter().filter(|i| i.can_reduce()) {
+                let action = Action::Reduce(item.production);
+                let prev = this_state.tokens.insert(item.lookahead, action);
+                if let Some(conflict) = prev {
+                    return Err(TableConstructionError {
+                        items: items.clone(),
+                        lookahead: item.lookahead,
+                        production: item.production,
+                        conflict: conflict,
+                    });
+                }
+            }
+
+            // extract a new state
+            states.push(this_state);
+        }
+
+        Ok(states)
+    }
+
+    fn items(&self,
+             id: NonterminalString,
+             index: usize,
+             lookahead: Lookahead)
+             -> Vec<Item<'grammar>>
+    {
+        self.grammar.productions_for(id)
+                    .iter()
+                    .map(|production| {
+                        debug_assert!(index <= production.symbols.len());
+                        Item { production: production,
+                                        index: index,
+                                        lookahead: lookahead }
+                    })
+                    .collect()
+    }
+
+    // expands `state` with epsilon moves
+    fn transitive_closure(&self, mut items: Vec<Item<'grammar>>)
+                          -> Items<'grammar>
+    {
+        let mut counter = 0;
+
+        let mut set: Set<Item<'grammar>> =
+            items.iter().cloned().collect();
+
+        while counter < items.len() {
+            let new_items: Vec<_> =
+                items[counter..]
+                .iter()
+                .filter_map(|item| {
+                    let shift_symbol = item.shift_symbol();
+                    match shift_symbol {
+                        None => None, // requires a reduce
+                        Some((Symbol::Terminal(_), _)) => None, // requires a shift
+                        Some((Symbol::Nonterminal(nt), remainder)) => {
+                            Some((nt, remainder, item.lookahead))
+                        }
+                    }
+                })
+                .flat_map(|(nt, remainder, lookahead)| {
+                    let first_set = self.first_sets.first(remainder, lookahead);
+                    first_set.into_iter()
+                             .flat_map(move |l| self.items(nt, 0, l))
+                })
+                .filter(|&item| set.insert(item))
+                .collect();
+
+            counter = items.len();
+            items.extend(new_items);
+        }
+
+        items.sort();
+        items.dedup();
+
+        Items { vec: Rc::new(items) }
+    }
+}
+
+

lalrpop/src/lr1/core/test.rs

@@ -2,9 +2,10 @@ use intern::intern;
 use generate;
 use grammar::repr::*;
 use test_util::{compare, expect_debug, normalized_grammar};
-use super::{build_states, State, Items, Lookahead, LR1};
+use lr1::Lookahead::EOF;
-use super::Lookahead::EOF;
+use lr1::interpret::interpret;
-use super::interpret::interpret;
+use lr1::core::{LR1, build_lr1_states};
+use lr1::{State, Items, Lookahead};
 
 fn nt(t: &str) -> NonterminalString {
     NonterminalString(intern(t))
@@ -12,7 +13,7 @@ fn nt(t: &str) -> NonterminalString {
 
 const ITERATIONS: usize = 22;
 
-fn random_test(grammar: &Grammar, states: &[State], start_symbol: NonterminalString) {
+fn random_test<'g>(grammar: &Grammar, states: &'g [State<'g>], start_symbol: NonterminalString) {
     for i in 0..ITERATIONS {
         let input_tree = generate::random_parse_tree(grammar, start_symbol);
         let output_tree = interpret(&states, input_tree.terminals()).unwrap();
@@ -117,7 +118,7 @@ grammar;
 
     // for now, just test that process does not result in an error
     // and yields expected number of states.
-    let states = build_states(&grammar, nt("S")).unwrap();
+    let states = build_lr1_states(&grammar, nt("S")).unwrap();
     assert_eq!(states.len(), 16);
 
     // execute it on some sample inputs.
@@ -185,5 +186,5 @@ fn shift_reduce_conflict1() {
         };
     "#);
 
-    assert!(build_states(&grammar, nt("E")).is_err());
+    assert!(build_lr1_states(&grammar, nt("E")).is_err());
 }

lalrpop/src/lr1/interpret.rs

@@ -7,27 +7,31 @@ use std::iter::IntoIterator;
 use std::fmt::{Debug, Display, Formatter, Error};
 use util::Sep;
 
-pub fn interpret<TOKENS>(states: &[State], tokens: TOKENS) -> Result<ParseTree, ()>
+pub type InterpretError<'grammar> = (&'grammar State<'grammar>, Lookahead);
+
+pub fn interpret<'grammar,TOKENS>(states: &'grammar [State<'grammar>], tokens: TOKENS)
+                         -> Result<ParseTree, InterpretError<'grammar>>
     where TOKENS: IntoIterator<Item=TerminalString>
 {
     let mut m = Machine::new(states);
     m.execute(tokens.into_iter())
 }
 
-struct Machine<'states, 'grammar:'states> {
+struct Machine<'grammar> {
-    states: &'states [State<'grammar>],
+    states: &'grammar [State<'grammar>],
-    state_stack: Vec<&'states State<'grammar>>,
+    state_stack: Vec<&'grammar State<'grammar>>,
     data_stack: Vec<ParseTree>,
 }
 
-impl<'states, 'grammar> Machine<'states, 'grammar> {
+impl<'grammar> Machine<'grammar> {
-    fn new(states: &'states [State<'grammar>]) -> Machine<'states,'grammar> {
+    fn new(states: &'grammar [State<'grammar>]) -> Machine<'grammar> {
         Machine { states: states,
                   state_stack: vec![],
                   data_stack: vec![] }
     }
 
-    fn execute<TOKENS>(&mut self, mut tokens: TOKENS) -> Result<ParseTree, ()>
+    fn execute<TOKENS>(&mut self, mut tokens: TOKENS)
+                       -> Result<ParseTree, InterpretError<'grammar>>
         where TOKENS: Iterator<Item=TerminalString>
     {
         assert!(self.state_stack.is_empty());
@@ -41,7 +45,7 @@ impl<'states, 'grammar> Machine<'states, 'grammar> {
 
             // check whether we can shift this token
             match state.tokens.get(&Lookahead::Terminal(terminal)) {
-                None => { return Err(()); }
+                None => { return Err((state, Lookahead::Terminal(terminal))); }
 
                 Some(&Action::Shift(next_index)) => {
                     self.data_stack.push(ParseTree::Terminal(terminal));
@@ -60,7 +64,7 @@ impl<'states, 'grammar> Machine<'states, 'grammar> {
         loop {
             let state = *self.state_stack.last().unwrap();
             match state.tokens.get(&Lookahead::EOF) {
-                None => { return Err(()); }
+                None => { return Err((state, Lookahead::EOF)); }
                 Some(&Action::Shift(_)) => { unreachable!("cannot shift EOF") }
                 Some(&Action::Reduce(production)) => {
                     if !self.reduce(production) {

lalrpop/src/lr1/la0/mod.rs

@@ -0,0 +1,151 @@
+//! Mega naive LALR(1) generation algorithm.
+
+use lr1::core;
+use grammar::repr::*;
+use std::rc::Rc;
+use util::{map, Map};
+use itertools::Itertools;
+use std::collections::hash_map::Entry;
+use super::{Action, State, StateIndex, Item, Items, Lookahead, TableConstructionError};
+use super::Action::{Reduce, Shift};
+
+#[cfg(test)]
+mod test;
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+struct LR0Item<'grammar> {
+    production: &'grammar Production,
+    index: usize
+}
+
+// Intermediate LALR(1) state. Identical to an LR(1) state, but that
+// the items can be pushed to. We initially create these with an empty
+// set of actions, as well.
+struct LALR1State<'grammar> {
+    index: StateIndex,
+    items: Vec<Item<'grammar>>,
+    tokens: Map<Lookahead, Action<'grammar>>,
+    gotos: Map<NonterminalString, StateIndex>,
+}
+
+pub fn lalr_states<'grammar>(grammar: &'grammar Grammar,
+                             start: NonterminalString)
+                             -> Result<Vec<State<'grammar>>, TableConstructionError<'grammar>>
+{
+    // First build the LR(1) states
+    let lr_states = try!(core::build_lr1_states(grammar, start));
+    collapse_to_lalr_states(&lr_states)
+}
+
+pub fn collapse_to_lalr_states<'grammar>(lr_states: &[State<'grammar>])
+                                         -> Result<Vec<State<'grammar>>,
+                                                   TableConstructionError<'grammar>>
+{
+    // Now compress them. This vector stores, for each state, the
+    // LALR(1) state to which we will remap it.
+    let mut remap: Vec<_> = (0..lr_states.len()).map(|_| StateIndex(0)).collect();
+    let mut lalr1_map: Map<Vec<LR0Item>, StateIndex> = map();
+    let mut lalr1_states: Vec<LALR1State> = vec![];
+
+    for (lr1_index, lr1_state) in lr_states.iter().enumerate() {
+        let lr0_kernel: Vec<_> =
+            lr1_state.items.vec.iter()
+                               .map(|item| LR0Item {
+                                   production: item.production,
+                                   index: item.index,
+                               })
+                               .dedup()
+                               .collect();
+
+        let lalr1_index =
+            *lalr1_map.entry(lr0_kernel)
+                      .or_insert_with(|| {
+                          let index = StateIndex(lalr1_states.len());
+                          lalr1_states.push(LALR1State {
+                              index: index,
+                              items: vec![],
+                              tokens: map(),
+                              gotos: map()
+                          });
+                          index
+                      });
+
+        lalr1_states[lalr1_index.0].items.extend(
+            lr1_state.items.vec.iter().cloned());
+
+        remap[lr1_index] = lalr1_index;
+    }
+
+    // Now that items are fully built, create the actions
+    for (lr1_index, lr1_state) in lr_states.iter().enumerate() {
+        let lalr1_index = remap[lr1_index];
+        let lalr1_state = &mut lalr1_states[lalr1_index.0];
+
+        for (&lookahead, &lr1_action) in &lr1_state.tokens {
+            let lalr1_action = match lr1_action {
+                Action::Shift(state) => Action::Shift(remap[state.0]),
+                Action::Reduce(prod) => Action::Reduce(prod),
+            };
+
+            match lalr1_state.tokens.entry(lookahead) {
+                Entry::Occupied(slot) => {
+                    let old_action = *slot.get();
+                    if old_action != lalr1_action {
+                        return Err(conflict(&lalr1_state.items, lookahead,
+                                            old_action, lalr1_action));
+                    }
+                }
+                Entry::Vacant(slot) => {
+                    slot.insert(lalr1_action);
+                }
+            }
+        }
+
+        for (&nt, &lr1_dest) in &lr1_state.gotos {
+            let lalr1_dest = remap[lr1_dest.0];
+
+            match lalr1_state.gotos.entry(nt) {
+                Entry::Occupied(slot) => {
+                    let old_dest = *slot.get();
+                    assert_eq!(old_dest, lalr1_dest);
+                }
+                Entry::Vacant(slot) => {
+                    slot.insert(lalr1_dest);
+                }
+            }
+        }
+    }
+
+    // Finally, create the new states
+    Ok(
+        lalr1_states.into_iter()
+                    .map(|lr| State {
+                        index: lr.index,
+                        items: Items { vec: Rc::new(lr.items) },
+                        tokens: lr.tokens,
+                        gotos: lr.gotos
+                    })
+                    .collect())
+}
+
+fn conflict<'grammar>(items: &[Item<'grammar>],
+                      lookahead: Lookahead,
+                      action1: Action<'grammar>,
+                      action2: Action<'grammar>)
+                      -> TableConstructionError<'grammar> {
+    let (production, conflict) = match (action1, action2) {
+        (c @ Shift(_), Reduce(p)) |
+        (Reduce(p), c @ Shift(_)) |
+        (Reduce(p), c @ Reduce(_)) => { (p, c) }
+        _ => {
+            panic!("conflict between {:?} and {:?}", action1, action2) 
+        }
+    };
+
+    TableConstructionError {
+        items: Items { vec: Rc::new(items.to_vec()) },
+        lookahead: lookahead,
+        production: production,
+        conflict: conflict,
+    }
+}

lalrpop/src/lr1/la0/test.rs

@@ -0,0 +1,41 @@
+use intern::intern;
+use generate;
+use grammar::repr::*;
+use test_util::{compare, expect_debug, normalized_grammar};
+use super::lalr_states;
+use super::super::interpret::interpret;
+
+fn nt(t: &str) -> NonterminalString {
+    NonterminalString(intern(t))
+}
+
+macro_rules! tokens {
+    ($($x:expr),*) => {
+        vec![$(TerminalString(intern($x))),*].into_iter()
+    }
+}
+
+#[test]
+fn figure9_23() {
+    let grammar = normalized_grammar(r#"
+        grammar;
+        extern token { enum Tok { } }
+        S: () = E       => ();
+        E: () = {
+            E "-" T     => ();
+            T           => ();
+        };
+        T: () = {
+            "N"         => ();
+            "(" E ")"   => ();
+        };
+   "#);
+
+    let states = lalr_states(&grammar, nt("S")).unwrap();
+    println!("{:#?}", states);
+
+    let tree = interpret(&states, tokens!["N", "-", "(", "N", "-", "N", ")"]).unwrap();
+    assert_eq!(
+        &format!("{:?}", tree)[..],
+        r#"[S: [E: [E: [T: "N"]], "-", [T: "(", [E: [E: [T: "N"]], "-", [T: "N"]], ")"]]]"#);
+}

lalrpop/src/lr1/mod.rs

@@ -4,23 +4,19 @@ use kernel_set;
 use grammar::repr::*;
 use std::fmt::{Debug, Formatter, Error};
 use std::rc::Rc;
-use util::{map, Map, Multimap, Set, Prefix};
+use util::{Map, Prefix};
 
 pub mod ascent;
 
+mod core;
 mod error;
 mod first;
+mod la0;
 
 #[cfg(test)] mod interpret;
-#[cfg(test)] mod test;
 
 pub use self::error::report_error;
 
-struct LR1<'grammar> {
-    grammar: &'grammar Grammar,
-    first_sets: first::FirstSets,
-}
-
 #[derive(Debug)]
 pub struct State<'grammar> {
     index: StateIndex,
@@ -29,7 +25,7 @@ pub struct State<'grammar> {
     gotos: Map<NonterminalString, StateIndex>,
 }
 
-#[derive(Debug)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 enum Action<'grammar> {
     Shift(StateIndex),
     Reduce(&'grammar Production),
@@ -75,137 +71,9 @@ pub fn build_states<'grammar>(grammar: &'grammar Grammar,
                               start: NonterminalString)
                               -> Result<Vec<State<'grammar>>, TableConstructionError<'grammar>>
 {
-    let lr1 = LR1::new(grammar);
+    match grammar.algorithm {
-    lr1.build_states(start)
+        Algorithm::LR1 => core::build_lr1_states(grammar, start),
-}
+        Algorithm::LALR1 => la0::lalr_states(grammar, start),
-
-impl<'grammar> LR1<'grammar> {
-    fn new(grammar: &'grammar Grammar) -> LR1 {
-        LR1 {
-            grammar: grammar,
-            first_sets: first::FirstSets::new(grammar),
-        }
-    }
-
-    fn build_states(&self, start_nt: NonterminalString)
-                    -> Result<Vec<State<'grammar>>, TableConstructionError<'grammar>>
-    {
-        let mut kernel_set = kernel_set::KernelSet::new();
-        let mut states = vec![];
-
-        // create the starting state
-        kernel_set.add_state(
-            self.transitive_closure(
-                self.items(start_nt, 0, Lookahead::EOF)));
-
-        while let Some(items) = kernel_set.next() {
-            let index = StateIndex(states.len());
-            let mut this_state = State { index: index, items: items.clone(),
-                                         tokens: map(), gotos: map() };
-
-            // group the items that we can transition into by shifting
-            // over a term or nonterm
-            let transitions: Multimap<Symbol, Item<'grammar>> =
-                items.vec
-                     .iter()
-                     .filter_map(|item| item.shifted_item())
-                     .collect();
-
-            for (symbol, items) in transitions.into_iter() {
-                let items = self.transitive_closure(items);
-                let next_state = kernel_set.add_state(items);
-
-                match symbol {
-                    Symbol::Terminal(s) => {
-                        let action = Action::Shift(next_state);
-                        let prev = this_state.tokens.insert(Lookahead::Terminal(s), action);
-                        assert!(prev.is_none()); // cannot have a shift/shift conflict
-                    }
-
-                    Symbol::Nonterminal(s) => {
-                        let prev = this_state.gotos.insert(s, next_state);
-                        assert!(prev.is_none());
-                    }
-                }
-            }
-
-            // finally, consider the reductions
-            for item in items.vec.iter().filter(|i| i.can_reduce()) {
-                let action = Action::Reduce(item.production);
-                let prev = this_state.tokens.insert(item.lookahead, action);
-                if let Some(conflict) = prev {
-                    return Err(TableConstructionError {
-                        items: items.clone(),
-                        lookahead: item.lookahead,
-                        production: item.production,
-                        conflict: conflict,
-                    });
-                }
-            }
-
-            // extract a new state
-            states.push(this_state);
-        }
-
-        Ok(states)
-    }
-
-    fn items(&self,
-             id: NonterminalString,
-             index: usize,
-             lookahead: Lookahead)
-             -> Vec<Item<'grammar>>
-    {
-        self.grammar.productions_for(id)
-                    .iter()
-                    .map(|production| {
-                        debug_assert!(index <= production.symbols.len());
-                        Item { production: production,
-                                        index: index,
-                                        lookahead: lookahead }
-                    })
-                    .collect()
-    }
-
-    // expands `state` with epsilon moves
-    fn transitive_closure(&self, mut items: Vec<Item<'grammar>>)
-                          -> Items<'grammar>
-    {
-        let mut counter = 0;
-
-        let mut set: Set<Item<'grammar>> =
-            items.iter().cloned().collect();
-
-        while counter < items.len() {
-            let new_items: Vec<_> =
-                items[counter..]
-                .iter()
-                .filter_map(|item| {
-                    let shift_symbol = item.shift_symbol();
-                    match shift_symbol {
-                        None => None, // requires a reduce
-                        Some((Symbol::Terminal(_), _)) => None, // requires a shift
-                        Some((Symbol::Nonterminal(nt), remainder)) => {
-                            Some((nt, remainder, item.lookahead))
-                        }
-                    }
-                })
-                .flat_map(|(nt, remainder, lookahead)| {
-                    let first_set = self.first_sets.first(remainder, lookahead);
-                    first_set.into_iter()
-                             .flat_map(move |l| self.items(nt, 0, l))
-                })
-                .filter(|&item| set.insert(item))
-                .collect();
-
-            counter = items.len();
-            items.extend(new_items);
-        }
-
-        items.sort();
-        items.dedup();
-
-        Items { vec: Rc::new(items) }
     }
 }
 

lalrpop/src/normalize/lower/mod.rs

@@ -88,6 +88,12 @@ impl LowerState {
                               .map(|p| r::Parameter { name: p.name, ty: p.ty.type_repr() })
                               .collect();
 
+        let algorithm =
+            match grammar.algorithm {
+                None => r::Algorithm::LR1,
+                Some(ref a) => r::Algorithm::from_str(a.text).unwrap(),
+            };
+
         Ok(r::Grammar {
             prefix: self.prefix,
             start_nonterminals: start_symbols,
@@ -100,6 +106,7 @@ impl LowerState {
             type_parameters: grammar.type_parameters,
             parameters: parameters,
             where_clauses: grammar.where_clauses,
+            algorithm: algorithm
         })
     }
 

lalrpop/src/normalize/prevalidate/mod.rs

@@ -4,6 +4,7 @@ use super::{NormResult, NormError};
 use super::norm_util::{self, Symbols};
 
 use grammar::parse_tree::*;
+use grammar::repr;
 use intern::{intern, InternedString};
 use util::{Map, Multimap, Sep, set};
 
@@ -55,6 +56,17 @@ struct ScopeChain<'scope> {
 
 impl<'grammar> Validator<'grammar> {
     fn validate(&self) -> NormResult<()> {
+        if let Some(ref algorithm) = self.grammar.algorithm {
+            match repr::Algorithm::from_str(algorithm.text) {
+                Some(_) => { }
+                None => {
+                    return_err!(
+                        algorithm.span,
+                        "unrecognized algorithm `{}`", algorithm.text);
+                }
+            }
+        }
+
         for item in &self.grammar.items {
             match *item {
                 GrammarItem::Use(..) => { }

lalrpop/src/parser/lrgrammar.lalrpop

@@ -12,6 +12,7 @@ pub Grammar: Grammar =
     <tps:GrammarTypeParameters?>
     <parameters:GrammarParameters?>
     <where_clauses:"where"?>
+    <algorithm:Algorithm?>
     ";"
     <items:GrammarItem*> => {
         let where_clauses =
@@ -25,7 +26,16 @@ pub Grammar: Grammar =
                   type_parameters: tps.unwrap_or(vec![]),
                   parameters: parameters.unwrap_or(vec![]),
                   where_clauses: where_clauses,
-                  items: uses.into_iter().chain(items).collect() }
+                  items: uses.into_iter().chain(items).collect(),
+                  algorithm: algorithm }
+    };
+
+Algorithm: Algorithm =
+    "[" <lo:@L> <t:StringLiteral> <hi:@R> "]" => {
+        Algorithm {
+            span: Span(lo, hi),
+            text: t
+        }
     };
 
 GrammarTypeParameters: Vec<TypeParameter> =